1. Field of the Invention
The invention relates to a method for manufacturing a semiconductor light emitting device and a semiconductor light emitting device. In particular, the invention relates to a semiconductor light emitting device and method for manufacturing a light emitting device that allows light to emit from a light emitting element through a wavelength conversion layer, mixes light emitted from the light emitting element for excitation with wavelength-converted light from the wavelength conversion layer, and then emits the light to the outside.
2. Detailed Description of the Related Art
Japanese Patent Laid-Open Publication No. 2004-119838 (JP'838) discloses an example of a conventional method for manufacturing an LED that is used as this type of wavelength conversion semiconductor light emitting device, and is shown in FIG. 1(A) and FIG. 1(B).
Namely, according to JP'838, a housing 1 is formed of a thermoplastic resin and has a light reflecting cavity 1a on the upper surface thereof as shown in FIG. 1(A). Lead frames 2 are insertion molded into the housing 1. The lead frames 2 are exposed on the bottom face inside the cavity 1a. 
At the bottom of the cavity 1a, an LED chip 3 is placed on one of the lead frames 2 and is electrically connected to both lead frames 2 by die bonding or wire bonding (not shown in the figure).
Thereafter, a first sealing resin 5 is applied to the inside of the cavity 1a up to approximately half the height thereof to cover the LED chip 3. Then, a second sealing resin 6 is applied over the first sealing resin 5. A fluorescent material 6a is contained in the second sealing resin 6 to function as a wavelength conversion material and includes a specified quantity of particles. The fluorescent material 6a within the second sealing resin 6 is prepared with a particle concentration that does not allow those particles to precipitate during application.
Further, as shown in FIG. 1(B), the particulate fluorescent material 6a inside the second sealing resin 6 precipitates and migrates downwards by their own weight to the first sealing resin 5.
Lastly, the LED is completed by hardening the first sealing resin 5 and the second sealing resin 6.
According to the manufacturing method of an LED with this type of configuration, the upper surface of the first sealing resin 5 is made to be almost flat by applying a first sealing resin 5 that has a comparatively low viscosity inside the cavity 1a and without the fluorescent material 6a. In addition, the concentration distribution of the fluorescent material 6a is made to be almost uniform in the horizontal direction by applying the second sealing resin 6 at an almost uniform thickness over the first sealing resin 5.
After this, the fluorescent material 6a within the second sealing resin 6 precipitates by its own weight. After the precipitation, the concentration of the fluorescent material 6a is almost uniform in the horizontal direction. Thus, light emitting characteristics that do not have uneven color can be obtained.
The manufacturing method of an LED with this type of configuration has the following types of problems.
Namely, the second sealing resin 6 is applied at an almost uniform thickness and the particles of the fluorescent material 6a contained within that resin 6 precipitate through the first sealing resin 5. The LED chip 3 however, exists close to the center of the cavity 1a. Because of this, the concentration distribution of the fluorescent material 6a in the direction of height causes a difference in level to occur between a location over the LED chip 3 and a location at the bottom face of the cavity 1a around the chip 3. This difference in level is equal to the height of the LED chip 3.
Also, the excitation intensity of the fluorescent material 6a positioned on the periphery of the LED chip 3 becomes smaller as the distance from the LED chip 3 becomes further, thereby resulting in a decrease in the conversion efficiency for the entire LED.
Even further, due to precipitation, the fluorescent material 6a is dispersed uniformly in two dimensions (flatly) at the upper portion of the LED chip 3 and around the chip 3 in its final disposition. It is a well-known fact that when the LED chip 3 emits blue light in three dimensions, and the fluorescent material 6a converts the blue light into yellow light, a mixed color of light consisting of the blue light from the LED chip 3 and the wavelength-converted light produced by the fluorescent material 6a becomes a somewhat bluish white over the LED chip 3, and becomes yellowish white around the periphery of the LED chip 3.
Additionally, the fluorescent material 6a generates heat due to energy loss during the wavelength conversion. When the fluorescent material 6a is allowed to precipitate, the particles of the fluorescent material 6a precipitate through the first sealing resin 5, resulting in a lowered density of the fluorescent material 6a after precipitation. Consequently, the heat generated from the fluorescent material 6a passes through the first sealing resin 5 and reaches the housing 1 made of a thermoplastic resin, thereby dissipating to the outside. This in turn results in an inefficient and poor dissipation of heat due to insufficient thermal conductivity of both the first sealing resin 5 and the housing 1.
This type of problem not only occurs with blue LED chips but also similarly exists in LED chips which emit other colors, as well as in semiconductor light emitting devices, such as LEDs, which emit a mixed color of light consisting of and/or comprising light from other light emitting elements and wavelength-converted light from wavelength conversion material.
In addition, this problem is not only with LEDs of the type in which the lead frames are insertion molded. For example, the same types of problems occurs in semiconductor light emitting devices, such as LEDs, in which a cavity is formed on the upper surface of a semiconductor substrate and wherein the LEDs are provided with electrode layers composed of a conductive thin film. For example, LEDs in which the film wraps around from the bottom face of the cavity up to the upper surface of the substrate through the sides of the cavity and, according to circumstances, down along the side surfaces of the substrate to the rear surface thereof.